Offline Coating Station

Coated paper, also known as gloss paper, is paper that has been treated with a mixture of materials or polymers to impart specific qualities such as increased weight, surface gloss, smoothness, or reduced ink absorbency. Materials used for coating paper include kaolinite, calcium carbonate, bentonite, and talc, making it suitable for high-quality printing in the packaging industry and magazines.

The chalk or china clay used in coating is bound to the paper with both synthetic and natural organic binders. The coating formulation may also include chemical additives like dispersants and resins to provide water resistance and wet strength to the paper.

Offline Coating

Chromo Paper and Board: This type of paper or board is primarily coated on one side of bleached base paper of various GSM. The coating provides high printing resolution and is mainly used for one-side coating on which printing takes place. This type of coating is typically done on an offline coater.

Art Paper and Board: This paper or board is coated on both sides of bleached base paper of various GSM. It is used for glossy magazines and high-end paper products like visiting cards, invitation cards, calendars, and brochures. This type of coating is usually performed on an offline coater. These paper grades are triple coated with 20–40 g/m² per side and have a matte or glossy finish.

Types of Coating Machines

All coating machines, except for the curtain coater, feature an applicator roll dipped in a color pan. A film of coating chemical slurry, with solid contents ranging from 50% to 65%, is transferred onto the paper sheet. To remove excess chemical and maintain uniform coating thickness, various devices are used:

• Air Knife: This non-contact type of scraper removes excess chemical and provides a uniform coating on the paper but is unable to fill the paper’s hills and valleys. It is mainly used for low GSM base paper.
• Blade-Bar Coater: The blade scraper is preferred for maintaining a perfect clearance between the paper and blade, ensuring all hills and valleys are filled with chemical, resulting in the best gloss on paper.
• Curtain Coater: In this machine, a film of coating chemical falls onto the running paper, utilizing the full chemical. It is highly sophisticated and used for high-speed operations. With one unit, three different chemicals can be applied. While the coating thickness is uniform, there is no evening effect if the paper is uneven, making it suitable for lower GSM well-calendared paper.